<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        /* Tips：仅仅发生在块级元素之间
                 子元素不设置宽度，他会继承父元素的宽度--（块）*/
      .parent{
          width: 200px;
          height: 200px;
          background: pink;
      }
      .child{
          height: 100px;
          background: darkcyan;
      }
    </style>
</head>
<body>
    <!-- width的继承-->
    <div class="parent">
     <div class="child">
     </div>
    </div>
</body>
</html>